Oxygen partial-pressure control unit and method of gas supply

ABSTRACT

The oxygen partial pressure control unit includes a gas purification section for purifying the gas having the oxygen partial pressure controlled within a range of from 0.2 to 10−30 atm, and a tank for storing the purified gas produced by the gas purification section. The purified gas stored within the tank is supplied to the another unit. The oxygen partial pressure control unit includes a circulation circuit including the tank and the gas purification section. The gas filled in the tank 20 is caused to circulate along the circulation circuit, and the purified gas produced by the gas purification section is stored in the tank.

TECHNICAL FIELD

The present invention relates to an oxygen partial pressure control unitand a gas supply method.

BACKGROUND ART

Conventionally, there is known a method in which a single crystal sampleor the like is prepared using an atmospheric gas that has an oxygenpartial pressure controlled by an oxygen partial pressure control unitprovided with an electrochemical oxygen pump containing a solidelectrolyte (Patent Document 1).

An oxygen partial pressure control unit illustrated in FIG. 9 includes amass flow controller (MFC) 3 that controls the flow rate of an inert gascoming through a valve 2 to a set value, an electrochemical oxygen pump4 capable of controlling the oxygen partial pressure of the inert gascoming through the mass flow controller 3 to a target value, and anoxygen sensor 5 for supply gas, which monitors the oxygen partialpressure of the inert gas, which has been controlled by the oxygen pump4, and supplies the gas to a subsequent process (unit) such as a samplepreparation unit.

This unit further includes an oxygen partial pressure setting section 6that sets a desired oxygen partial pressure value, an oxygen partialpressure control section 7 that compares a monitor value of the oxygensensor 5 with the set value of the oxygen partial pressure settingsection 6 to control the oxygen partial pressure of the inert gas to besent from the oxygen pump 4 to a predetermined value, and an oxygenpartial pressure display section 8 that displays the monitor value ofthe oxygen sensor 5. It should be noted that the oxygen partial pressureof the inert gas is normally approximately 10⁻⁴ atm.

As illustrated in FIG. 10, in the electrochemical oxygen pump 4,electrodes 4 b and 4 c made of platinum are formed on both the innersurface and the outer surface of a solid electrolytic cylindrical body 4a having oxide ion conductivity. The solid electrolytic cylindrical body4 a is, for example, a zirconia-based solid electrolyte, and is heatedby a heater (not shown). The inert gas is supplied in the axialdirection from one opening of the solid electrolytic cylindrical body 4a to the other opening thereof. The inert gas is, for example, Ar+O₂(10⁻⁴ atm). The DC voltage of a DC power supply E is applied between theelectrodes 4 b and 4 c disposed on both the inner and outer surfacesthereof. When a positive voltage is applied to the electrode 4 cdisposed on the outer surface and a negative voltage is applied to theelectrode 4 b disposed on the inner surface to cause a current I toflow, oxygen molecules (O₂) within the inert gas flowing through thesolid electrolytic cylindrical body 4 a are electrically reduced intoions (O²⁻), and then are released via the solid electrolyte to theoutside of the solid electrolytic cylindrical body 4 a as oxygenmolecules (O₂) again. The oxygen molecules released to the outside ofthe solid electrolytic cylindrical body 4 a are discharged along withauxiliary gases such as air. The inert gas Ar+O₂ (10⁻⁴ atm) supplied tothe solid electrolytic cylindrical body 4 a is converted, with theoxygen molecules reduced in number, into a processed gas (purified gas)that has the oxygen partial pressure controlled to a target value, andthen is fed to the subsequent process (unit).

It should be noted that the oxygen pump 4 of FIG. 10 is capable ofperforming the pump operation also when a DC voltage having the oppositepolarity to the above-mentioned case is applied between the electrodes 4b and 4 c disposed on both the inner and outer surfaces of the solidelectrolytic cylindrical body 4 a. Specifically, when a negative voltageis applied to the electrode 4 c disposed on the outer surface and apositive voltage is applied to the electrode 4 b disposed on the innersurface, oxygen molecules (O₂) in gas, such as air, flowing along theouter surface of the solid electrolytic cylindrical body 4 a areelectrically reduced into ions (O²⁻) via the solid electrolyte, and thenreleased via the solid electrolyte to the inside of the solidelectrolytic cylindrical body 4 a as oxygen molecules (O₂) again. Inthis case, the oxygen partial pressure of the inert gas flowing insidethe solid electrolytic cylindrical body 4 a is increased, and the inertgas is fed to the outside.

By supplying a gas that has the oxygen partial pressure controlled bysuch an oxygen pump, it becomes possible to perform crystal growth,alloying, heat treatment, a semiconductor manufacturing process, and thelike, under an inert gas atmosphere having a controlled oxygen partialpressure.

Patent Document 1: JP 2002-326887 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The oxygen pump illustrated in FIG. 10 uses one solid electrolyticcylindrical body in a shape of a circular pipe. Specifically, a gas tobe processed is caused to flow in the axial direction within the innerspace of this one solid electrolytic cylindrical body, and while the gasis flowing within the solid electrolytic cylindrical body, a pumpingaction is performed through ion conduction between the inside andoutside of the diaphragm of the solid electrolyte. The flow rate of thegas, which can be processed by such a gas pump, is proportional to thearea of contact between the gas to be processed and the inner and outersurfaces of the solid electrolytic cylindrical body. Accordingly, if theflow rate of the gas is to be increased, it is necessary to increase thearea of contact between the gas to be processed and the outer surface ofthe solid electrolytic cylindrical body.

For that purpose, lengthening the solid electrolytic cylindrical body orincreasing the diameter of the pipe is conceivable. In order toeffectively use an oxygen ion conductive solid electrolyte, it isnecessary to lower the resistance value of the oxygen pump as much aspossible and to enhance the oxygen permeability of the oxygen pump. Theresistance value of the oxygen pump is affected by the shape (surfacearea and thickness) of the solid electrolyte, the electrode film, thelead terminal, and the like. Of those factors, as to the shape of thesolid electrolyte, the resistance value becomes smaller as the surfacearea becomes larger and the solid electrolyte becomes thinner.Specifically, for a cylindrical body, it is desirable that the diameterand length thereof be larger and the thickness thereof be smaller.However, for the ease with which the solid electrolytic cylindrical bodyis manufactured and the strength of the solid electrolytic cylindricalbody to be used in a heated/high-temperature state, there arelimitations in terms of the diameter, the length, and the thickness.Further, as the diameter of the pipe becomes larger, the number of ionconduction reactions sharply declines in the gas to be processed, whichis flowing in the core portion of the solid electrolytic cylindricalbody. As a result, the gas to be processed, which is flowing in the coreportion, passes through without having any reactions, which results indeclined control accuracy with respect to the oxygen partial pressureand the like. For this reason, as a matter of course, there is alimitation to simply increasing the diameter of the pipe of the solidelectrolytic cylindrical body. This means that the above-mentionedmethod has a limit on increasing the area of contact between the gas tobe processed and the solid electrolytic cylindrical body. Thus, the flowrate of the gas, which can be substantially effectively processed by thegas pump, has been limited, and applications for supply of the gashaving a controlled oxygen partial pressure have been limited.

In view of the above-mentioned problems, the present invention has beenmade, and therefore has an object to provide an oxygen partial pressurecontrol unit and a gas supply method, which are capable of supplying, toanother unit such as a sample preparation chamber, a gas (purified gas)that has a controlled oxygen partial pressure without causing a shortagethereof, and allow the another unit to efficiently perform an operation(sample preparation operation) that uses the purified gas.

Means for Solving the Problems

According to the present invention, an oxygen partial pressure controlunit includes: a gas purification section for purifying a gas having anoxygen partial pressure controlled within a range of from 0.2 to 10⁻³⁰atm; and a tank for storing the purified gas produced by the gaspurification section, the oxygen partial pressure control unit supplyingthe purified gas stored within the tank to another unit, in which theoxygen partial pressure control unit further includes a circulationcircuit including the tank and the gas purification section, and asource gas filled in the tank is caused to circulate along thecirculation circuit, and the purified gas produced by the gaspurification section is stored in the tank.

With the oxygen partial pressure control unit of the present invention,the source gas filled in the tank is caused to circulate along thecirculation circuit, and the purified gas produced by the gaspurification section can be stored in the tank. Therefore, it ispossible to provide stable supply of the purified gas to the anotherunit.

The circulation circuit includes: a plurality of the tanks; a firstswitching means for switching between permission and suspension ofsupply of the purified gas produced by the gas purification section toeach of the plurality of the tanks; and a second switching means forswitching between the permission and the suspension of the supply of thepurified gas of the each of the plurality of the tanks to the anotherunit. The circulation circuit is configured to: switch the secondswitching means to permit the supply of the purified gas from at leastone of the plurality of the tanks to the another unit; and switch thefirst switching means to produce the purified gas for the tank that hasfinished the supply of the purified gas to the another unit, with thesupply of the gas from the at least one of the plurality of the tankspermitted.

The purified gas can be stored in the plurality of the tanks, and henceit is possible to improve the capacity for supplying the purified gas tothe another unit. In addition, with the switching of the secondswitching means, it is possible to supply the purified gas from the atleast one of the plurality of the tanks to the another unit, and, withthe switching of the first switching means, it is possible to supply thepurified gas produced by the gas purification section to the tank thathas finished the supply of the purified gas to the another unit.Further, at the time of supplying the gas from the at least one of theplurality of the tanks to the another unit, it is possible to producethe purified gas for the tank that has finished the supply of thepurified gas. Therefore, it is possible to supply the purified gascontinuously to the another unit without causing a shortage thereof.

The circulation circuit includes: a plurality of the gas purificationsections; and a third switching means for switching between permissionand suspension of supply of the purified gas from each of the pluralityof the gas purification sections to the tank. With the switching of thethird switching means, the circulation circuit can cause the gas tocirculate through a desired gas purification section among the pluralityof the gas purification sections.

With the provision of the plurality of the gas purification sections, itis possible to increase the gas purification capacity, enabling stablesupply of the purified gas to the another unit. In addition, with theswitching of the third switching means, it is possible to cause the gasto circulate through the desired gas purification section among theplurality of the gas purification sections. Therefore, for example, whendemand for the purified gas is low, the purified gas can be produced byone gas purification section, and, when the demand for the purified gasis high, the purified gas can be produced by a plurality of the gaspurification sections.

The circulation circuit includes: a plurality of the tanks; a pluralityof the gas purification sections; a first switching means for switchingbetween permission and suspension of supply of the purified gas producedby the gas purification sections to each of the plurality of the tanks;a second switching means for switching between the permission and thesuspension of the supply of the purified gas of the each of theplurality of the tanks to the another unit; and a third switching meansfor switching between the permission and the suspension of the supply ofthe purified gas from each of the plurality of the gas purificationsections to the plurality of the tanks. The circulation circuit isconfigured to: switch the second switching means to permit the supply ofthe purified gas from at least one of the plurality of the tanks to theanother unit; switch the first switching means to produce the purifiedgas for the tank that has finished the supply of the purified gas to theanother unit, with the supply of the gas from the at least one of theplurality of the tanks permitted; and switch the third switching meansto cause the gas to circulate through a desired gas purification sectionamong the plurality of the gas purification sections.

The purified gas can be stored in the plurality of the tanks, and henceit is possible to improve the capacity for supplying the purified gas tothe another unit. With the provision of the plurality of the gaspurification sections, it is possible to increase the gas purificationcapacity, enabling stable supply of the purified gas to the anotherunit. In addition, it is possible to produce the purified gas for thetank that has finished the supply of the purified gas to the anotherunit, with the supply of the gas from the tank permitted, enablingcontinuous supply of the purified gas to the another unit withoutcausing a shortage thereof. Further, the purified gas can be produced byone gas purification section, or can be produced by a plurality of thegas purification sections.

The gas purification section includes: an electrochemical oxygen pumpcapable of controlling an inert gas to a target oxygen partial pressure;and an oxygen sensor for monitoring the oxygen partial pressure of theinert gas. Further, the oxygen sensor can be disposed upstream anddownstream of the oxygen pump.

According to the present invention, a gas supply method of supplying, toanother unit, a purified gas having an oxygen partial pressurecontrolled within a range of from 0.2 to 10⁻³⁰ atm includes: supplying,after storing the purified gas in a plurality of tanks, the purified gasfrom at least one of the plurality of tanks to the another unit;supplying, after finishing the supplying the gas from the at least oneof the plurality of tanks, the purified gas from another one of theplurality of tanks to the another unit; and storing the purified gas inthe tank that has finished the supplying the gas during the supplyingthe purified gas.

With the gas supply method of the present invention, after stored in theplurality of tanks, the purified gas can be supplied from the at leastone of the plurality of tanks to the another unit. After the supplyingthe purified gas to the another unit is finished, the purified gas issupplied from the another one of the plurality of tanks to the anotherunit. Further, for the tank that has run short of the purified gas, thepurified gas can be supplied to and stored in that tank during thesupplying the purified gas from the another one of the plurality oftanks.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to store in the tankthe purified gas produced by the gas purification section, enablingstable supply of the purified gas to the another unit. In addition, thepurified gas is produced from the gas circulating within the circulationcircuit, and hence it is possible to produce the purified gas in a cleanstate, enabling the supply of the purified gas of high quality to theanother unit. In other words, with a unit in which the purified gas thathas been supplied to the another unit and used is returned andsequentially supplied to the gas purification section, it is difficultto maintain the clean state, and there is a fear of deterioratedquality.

The purified gas can be stored in a plurality of the tanks, and hence itis possible to enhance the capacity for supplying the purified gas tothe another device. With the provision of a plurality of the gaspurification sections, it is possible to increase the gas purificationcapacity, enabling stable supply of the purified gas to the anotherunit. Therefore, it is also possible to handle satisfactorily a unitthat requires a large amount of the purified gas, making applicationsfor the gas supply free from limitation.

In addition, with the switching of the first switching means and thesecond switching means, for a tank that has run short of the purifiedgas, the purified gas can be stored in that tank during the supplying ofthe gas from the another tank. Therefore, the purified gas can becontinuously supplied to the another unit, and the another unit canstably perform processing that uses the purified gas.

With the switching of the third switching means, it is possible tochange the number of the gas purification sections through which the gascirculates, enabling the gas purification capacity to be changed.Therefore, by changing the purification capacity in accordance with theamount of the gas to be used by the another unit of a supply target orthe like, it is possible to perform an efficient operation.

The gas purification section includes the electrochemical oxygen pumpcapable of controlling the oxygen partial pressure of the gas to atarget value, and the oxygen sensor that monitors the oxygen partialpressure of the gas. Specifically, the gas having the oxygen partialpressure controlled to the target value can be produced by the oxygenpump, and also, the oxygen partial pressure of this purified gas can bechecked. As a result, the gas having the oxygen partial pressurecontrolled to the target value can be stably supplied to the tank.Further, by disposing the oxygen sensors upstream and downstream of theoxygen pump, it becomes easier to regulate the gas purified by theoxygen pump, enabling the purification of the gas having the oxygenpartial pressure controlled more accurately.

With the gas supply method of the present invention, for a tank that hasrun short of the purified gas, the purified gas can be stored in thattank during the supplying of the gas from the another tank. Therefore,the purified gas can be continuously supplied to the another unit, andthe another unit can stably perform the processing that uses thepurified gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A simplified schematic view of an oxygen partial pressure controlunit representing an embodiment of the present invention.

FIG. 2 A simplified schematic view of the oxygen partial pressurecontrol unit representing a process of filling a tank with a source gas.

FIG. 3 A simplified schematic view of the oxygen partial pressurecontrol unit representing a process of gas purification.

FIG. 4 A simplified schematic view of the oxygen partial pressurecontrol unit representing a process of supplying a purified gas from afirst tank to a sample preparation chamber and a purification process ofa second tank.

FIG. 5 A simplified schematic view of the oxygen partial pressurecontrol unit representing a process of supplying the purified gas fromthe second tank to the sample preparation chamber and a process offilling the first tank with a gas.

FIG. 6 A simplified schematic view of the oxygen partial pressurecontrol unit representing the process of supplying the purified gas fromthe second tank to the sample preparation chamber and a process ofpurifying the gas of the first tank.

FIG. 7 A simplified schematic view of the oxygen partial pressurecontrol unit representing the process of supplying the purified gas fromthe first tank to the sample preparation chamber and a process offilling the second tank with the source gas.

FIG. 8 A simplified schematic view of the oxygen partial pressurecontrol unit representing another embodiment of the present invention.

FIG. 9 A simplified schematic view of a conventional oxygen partialpressure control unit.

FIG. 10 An explanatory view of a principle of an oxygen pump.

DESCRIPTION OF REFERENCE SYMBOLS

-   -   14 oxygen pump    -   15A oxygen sensor    -   15B oxygen sensor    -   19, 19A, 19B circulation circuit    -   20, 20A, 20B tank    -   21, 21A, 21B gas purification section    -   51 first switching means    -   52 second switching means    -   76 third switching means

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates an oxygen partial pressure control unit according tothe present invention. This oxygen partial pressure control unit, whichis provided with a circulation circuit 19 including a plurality of (inthe example of FIG. 1, two) tanks (buffer tanks) 20A and 20B and a gaspurification section 21 that purifies a gas having an oxygen partialpressure controlled within a range of from 0.2 to 10⁻³⁰ atm, fills thetanks 20A and 20B with the purified gas produced by the gas purificationsection 21, and then supplies the purified gas from the tanks 20A and20B to another unit (for example, sample preparation chamber).

The gas purification section 21 includes an electrochemical oxygen pump14 capable of controlling the gas to have a target oxygen partialpressure, an upstream oxygen sensor 15A that monitors the oxygen partialpressure of an inert gas before the inert gas flows into the oxygen pump14, and a downstream oxygen sensor 15B that monitors the oxygen partialpressure of the gas, which is controlled by the oxygen pump 14. Further,upstream of the upstream oxygen sensor 15A, there are disposed apressure regulating valve (REG) 22 that regulates the pressure of thegas coming through a switching valve 12, and a mass flow controller(MFC) 13 that controls the flow rate of the gas coming through thepressure regulating valve (REG) to a set value.

For the oxygen pump 14, a configuration in which electrodes made ofplatinum are formed on both the inner surface and the outer surface of asolid electrolytic cylindrical body having oxide ion conductivity, thatis, a configuration the same as that of an oxygen pump 4 illustrated inFIG. 10, may be employed. Accordingly, a description of theconfiguration and principle of the oxygen pump 14 is herein omitted.

For the oxygen sensors 15A and 15B, similarly to the above-mentionedoxygen pump 14, the configuration in which electrodes made of platinumare formed on both the inner surface and the outer surface of a solidelectrolytic cylindrical body having oxide ion conductivity may beemployed. Then, a potential difference between the electrode on theinner surface and the electrode on the outer surface is measured,whereby the oxygen partial pressure can be determined by the Nernstequation of thermodynamics.

Further, this oxygen partial pressure control unit includes: an oxygenpartial pressure setting section 16 that sets a desired oxygen partialpressure value; an oxygen partial pressure control section 17, such as aPID control system, which compares monitor values of the upstream oxygensensor 15A and the downstream oxygen sensor 15B with a set value of theoxygen partial pressure setting section 16, and then controls the oxygenpartial pressure of the gas to be sent from the oxygen pump 14 to apredetermined value; and an oxygen partial pressure display section 18that displays the oxygen partial pressure set value of theabove-mentioned oxygen partial pressure setting section 16, and themonitor values of the oxygen sensors 15A and 15B.

An outlet side of the gas purification section 21 is connected to a pairof the tanks 20A and 20B via a first circulation path 25, whereas aninlet side of the gas purification section 21 is connected to the pairof the tanks 20A and 20B via a second circulation path 26.

The first circulation path 25 includes a main body pipe 29 in which aflow rate regulating valve 27 and a pump (for example, diaphragm pump)28 are interposed, and first and second branch pipes 30 a and 30 bbranching from the main body pipe 29. It should be noted that switchingvalves 31 and 32 are interposed in the branch pipes 30 a and 30 b,respectively.

The second circulation path 26 includes a main body pipe 34 in which aswitching valve 33 is interposed, and first and second branch pipes 35 aand 35 b branching from the main body pipe 34. It should be noted thatswitching valves 36 and 37 are interposed in the branch pipes 35 a and35 b, respectively.

The second circulation path 26 is connected to an outflow path 38 forsupplying the purified gas into another unit (for example, samplepreparation chamber or the like). The outflow path 38 includes adownstream pipe 40 in which an MFC 39 is interposed, a connecting pipe41 a connecting the downstream pipe 40 and the first branch pipe 35 a ofthe second circulation path 26, and a connecting pipe 41 b connectingthe downstream pipe 40 and the second branch pipe 35 b of the secondcirculation path 26. Pressure regulating valves (REGs) 42 and 43 andswitching valves 44 and 45 are interposed in the connecting pipes 41 aand 41 b, respectively.

Next, a description is made of an operation of the oxygen partialpressure control unit illustrated in FIG. 1. In this case, there areprovided: a process of filling each of the tanks 20A and 20B with asource gas as is illustrated in FIG. 2; a process of purifying thesource gas of each of the tanks 20A and 20B with the oxygen partialpressure controlled within a range of from 0.2 to 10⁻³⁰ atm as isillustrated in FIG. 3; a process of emitting (supplying) the purifiedgas of the first tank 20A to the sample preparation chamber or the like,and, at the same time, purifying the source gas of the second tank 20Binto the purified gas as is illustrated in FIG. 4; a process of fillingthe first tank 20A with the source gas, and, at the same time, emitting(supplying) the purified gas of the second tank 20B to the samplepreparation chamber or the like as is illustrated in FIG. 5; a processof purifying the gas of the first tank 20A, and, at the same time,emitting (supplying) the purified gas of the second tank 20B to thesample preparation chamber or the like as is illustrated in FIG. 6; anda process of emitting (supplying) the purified gas of the first tank 20Ato the sample preparation chamber or the like, and, at the same time,filling the second tank 20B with the source gas as is illustrated inFIG. 7. It should be noted that, in FIGS. 2 to 7, the illustration ofthe oxygen partial pressure control section 17 and the like is omitted.Further, in FIGS. 2 to 7, with regard to the switching valves 12, 31,32, 33, 36, 37, 44, and 45, a hollow mark indicates an open state, and afilled-in mark indicates a closed state. With regard to the circulationcircuit 19, the gas outflow path 38, and a gas inflow path 24, a thickline indicates that the gas is flowing.

In the process illustrated in FIG. 2, with the switching valves 31 and32 of the first circulation path 25 set to the open state, and theswitching valves 33, 36, 37, 44, and 45 of the second circulation path26 set to the closed state, the pump 28 is driven. With this, the sourcegas (process gas) passes through the switching valve 12 of the gasinflow path 24, and then flows into the first circulation path 25 viathe gas purification section 21.

Then, the source gas flows into the main body pipe 29 of the firstcirculation path 25, and then, the flow rate thereof is regulated by theflow rate regulating valve 27. Then, the source gas flows into thebranch paths 30 a and 30 b of the first circulation path 25 via the pump28, and then flows into the tanks 20A and 20B from the branch paths 30 aand 30 b, respectively. The switching valves 36, 37, 44, and 45 of thesecond circulation path 26 are in the closed state, and hence the sourcegas that has flowed into the tanks 20A and 20B does not flow out to thesecond circulation path 26. Specifically, the source gas, which has notbeen processed yet, flows through the gas inflow path 24, the gaspurification section 21 and the first circulation path 25 to the tanks20A and 20B as indicated by arrows A, and is sequentially supplied tothe tanks 20A and 20B, filling the tanks 20A and 20B.

In this manner, once the tanks 20A and 20B are filled with the sourcegas, the state illustrated in FIG. 2 is changed to a state illustratedin FIG. 3, in which the switching valve 12 is set to the closed state,and the switching valves 33, 36, and 37 of the second circulation path26 are set to the open state.

With this, there is formed the circulation circuit 19 including thetanks 20A and 20B, the second circulation path 26, the gas purificationsection 21, and the first circulation path 25. With the pump 28 driven,the gas circulates within the circulation circuit 19 as indicated byarrows B.

In this state, the gas purification section 21 purifies the gas flowingthrough the gas purification section 21. Specifically, the oxygenpartial pressure setting section 16 sets the oxygen partial pressure toa desired value, for example, 1×10⁻²¹ to 1×10⁻³⁰ atm. Then, a controlsignal for setting the oxygen partial pressure to the value set by theoxygen partial pressure setting section 16 is sent from the oxygenpartial pressure control section 17 to the oxygen pump 14. The controlsignal controls a current I of the oxygen pump 14, and the oxygenpartial pressure of the gas supplied to the oxygen pump 14 through theREG 22 and the mass flow controller (MFC) 13 is controlled toapproximately 1×10⁻²¹ to 1×10⁻³⁰ atm, which is set by the oxygen partialpressure setting section 16.

The gas flowing through the gas purification section 21 is monitored bythe upstream oxygen sensor 15A and the downstream oxygen sensor 15B forthe oxygen partial pressure thereof, and then, the monitor valuesthereof are displayed in the oxygen partial pressure display section 18and also input to the oxygen partial pressure control section 17. Inthis manner, the monitor values monitored by the oxygen sensors 15A and15B are input to the oxygen partial pressure control section 17, andthen compared with the set value set by the oxygen partial pressuresetting section 16. As a result, it is checked whether or not the oxygenpartial pressure of the gas, which is controlled by the oxygen pump 14,is controlled to be the set value by the oxygen partial pressure settingsection 16. Then, if the oxygen partial pressure monitored by the oxygensensor 15B does not coincide with the oxygen partial pressure set by theoxygen partial pressure setting section 16, a control signal is outputfrom the oxygen partial pressure control section 17 to the oxygen pump14, and the current I flowing through the oxygen pump 14 is regulated,whereby a gas (purified gas) having the oxygen partial pressurecontrolled to approximately 1×10⁻²¹ to 1×10⁻³⁰ atm is supplied to thefirst circulation path 25.

Due to this, the purified gas is supplied to the tanks 20A and 20B, andthe gas (mixed gas of purified gas and unprocessed source gas) flows outof the tanks 20A and 20B to the second circulation path 26 by the amountcorresponding to the amount of the gas that has flowed into the tanks20A and 20B, causing that gas to flow through the gas purificationsection 21 again. With this, the oxygen partial pressure of the gasflowing into the gas purification section 21 is controlled toapproximately 1×10⁻²¹ to 1×10⁻³⁰ atm, and the resultant gas (purifiedgas) is supplied to the first circulation path 25. In other words, withthe gas flowing within the circulation circuit 19, the gas purified tohave the oxygen partial pressure controlled to approximately 1×10⁻²¹ to1×10⁻³⁰ atm is supplied to the tanks 20A and 20B.

In this manner, when the gas of the tanks 20A and 20B has been purified,the purified gas of each of the tanks 20A and 20B is sent to the samplepreparation chamber. In this case, as illustrated in FIG. 4, thepurified gas of the first tank 20A is first emitted to the samplepreparation chamber. Specifically, from the state illustrated in FIG. 3,as illustrated in FIG. 4, the switching valve 31 of the firstcirculation path 25 is set to the closed state, and the switching valve36 and switching valve 44 of the second circulation path 26 are set tothe closed state and the open state, respectively.

With this, the purified gas of the first tank 20A at positive pressureflows out to the first connecting pipe 41 a of the outflow path 38.Then, the purified gas is emitted to the sample preparation chamber viathe mass flow controller (MFC) 39 that controls the flow rate of thepurified gas coming through the pressure regulating valve (REG) 42 to aset value. Specifically, the purified gas of the first tank 20A flowsalong the outflow path 38 as indicated by arrows C1, and then issupplied to the sample preparation chamber.

Further, the gas within the tank 20B circulates, as indicated by arrowsB1, along a circulation circuit 19B including the second tank 20B, thebranch pipe 35 b, the main body pipe 34, the gas purification section21, the main body pipe 29, and the branch pipe 30 b, with the resultthat the gas purification is continued.

When the supply of the purified gas of the first tank 20A to the samplepreparation chamber is finished, as illustrated in FIG. 5, the purifiedgas of the second tank 20B at positive pressure is emitted to the samplepreparation chamber. Specifically, from the state illustrated in FIG. 4,as illustrated in FIG. 5, the switching valve 31 of the firstcirculation path 25 is set to the open state, and the switching valve 32thereof is set to the closed state. Further, the switching valves 33,37, and 44 of the second circulation path 26 are set to the closedstate, and the switching valve 45 thereof is set to the open state.

With this, the purified gas of the second tank 20B flows out to thefirst connecting pipe 41 b of the outflow path 38. Then, the purifiedgas is emitted to the sample preparation chamber via the mass flowcontroller (MFC) 39 that controls the flow rate of the gas comingthrough the pressure regulating valve (REG) 43 to the set value.Specifically, the purified gas of the second tank 20B flows along theoutflow path 38 as indicated by arrows C2, and then is supplied to thesample preparation chamber.

Further, in the state illustrated in FIG. 5, the source gas is suppliedto the gas inflow path 24. Specifically, as indicated by arrows A1, thesource gas flows through the gas inflow path 24, the gas purificationsection 21, and the main body pipe 29 and the branch pipe 30 a of thefirst circulation path 25 to the first tank 20A to be supplied to thefirst tank 20A, whereby the first tank 20A is filled with the sourcegas.

Next, as illustrated in FIG. 6, the source gas filled in the first tank20A is purified. Specifically, from the state illustrated in FIG. 5, asillustrated in FIG. 6, the switching valves 36 and 33 of the secondcirculation path 26 are set to the open state. With this, the gascirculates, as indicated by arrows B2, along a circulation circuit 19Aincluding the first tank 20A, the branch pipe 35 a and main body pipe 34of the second circulation path 26, the gas purification section 21, andthe main body pipe 29 and branch pipe 30 a of the first circulation path25.

Owing to this circulation, the gas of the first tank 20A is purifiedagain. During the gas purification, the purified gas of the second tank205 flows along the outflow path 38 as indicated by the arrows C2, andis supplied to the sample preparation chamber.

Further, when the supply of the purified gas of the second tank 20B tothe sample preparation chamber is finished, as illustrated in FIG. 7,the second tank 20B is filled with the source gas again. Specifically,from the state illustrated in FIG. 6, as illustrated in FIG. 7, theswitching valve 31 of the first circulation path 25 is set to the closedstate, and the switching valve 32 thereof is set to the open state.Further, the switching valves 33, 36, and 45 of the second circulationpath 26 are set to the closed state, and the switching valve 44 thereofis set to the open state.

With this, as indicated by arrows A2, the source gas flows through thegas inflow path 24, the gas purification section 21, and the main bodypipe 29 and the branch pipe 30 b of the first circulation path 25 to thesecond tank 20B to be supplied to the second tank 20B, whereby thesecond tank 20B is filled with the source gas.

Further, while the second tank 20B is being filled with the source gas,the purified gas flows out from the first tank 20A to the connectingpipe 41 a of the gas outflow path 38. Specifically, the purified gas ofthe first tank 20A flows along the outflow path 38 as indicated by thearrows C1, and is supplied to the sample preparation chamber.Subsequently, the processing returns to the process illustrated in FIG.4, and the above-mentioned processes are repeated until the unit stopsoperating.

In this manner, the purified gas having the oxygen partial pressurecontrolled to 2×10⁻¹ to 1×10⁻³⁰ atm is continuously supplied to thesample preparation chamber.

According to the present invention, the purified gas that has beenproduced by the gas purification section 21 can be stored in the tank20, and hence it is possible to provide stable supply of the purifiedgas to another unit. Moreover, the purified gas is produced from the gascirculating within the circulation circuit 19, and hence it is possibleto produce the purified gas in a clean state, enabling a purified gas ofhigh quality to be supplied to another unit. In other words, with a unitin which the purified gas that has been supplied to another unit andused is returned and sequentially supplied to the gas purificationsection 21, it is difficult to maintain the clean state, and there is afear of deteriorated quality. In addition, the purified gas can bestored in a plurality of the tanks 20, and hence it is possible toenhance the capacity to supply the purified gas to another unit.

Then, the switching valves 31 and 32 and the like form a first switchingmeans 51 for switching between permission and suspension of the supplyof the purified gas produced by the gas purification section 21 to therespective tanks, whereas the switching valves 36, 37, 44, and 45 andthe like form a second switching means 52 for switching between thepermission and the suspension of the supply of the purified gas storedwithin the respective tanks 20A and 20B to another unit.

Accordingly, switching of the first switching means 51 and the secondswitching means 52 (in this case, formed by the switching valves 31, 32,36, 44, and the like) permits the supply of the purified gas from thefirst tank 20A to another unit (sample preparation chamber or the like),and switching of the first switching means 51 and the second switchingmeans 52 (in this case, formed by the switching valves 31, 32, 33, 37,45, and the like) enables the second tank 20B that has finishedsupplying the purified gas to another unit to be filled with the sourcegas, and enables the purification by the gas purification section 21, ina state in which the supply of the gas from the first tank 20A ispermitted.

In other words, according to the present invention, the switching of thefirst switching means 51 and the second switching means 52 enables thegas purified through circulating within the unit to be continuouslyemitted to another unit. As a result, processing that uses the purifiedgas is stably performed by another unit. It should be noted that thefirst switching means 51 and the second switching means 52 can berespectively formed with combinations of switching valves arbitrarilyselected from among the switching valves 31, 32, 33, 36, 37, 44, and 45and the like.

The gas purification section 21 includes the electrochemical oxygen pump14 capable of controlling the source gas to have the target oxygenpartial pressure, and the oxygen sensor 15 that monitors the oxygenpartial pressure of the gas. In other words, the gas having the oxygenpartial pressure controlled to the target value can be purified by theoxygen pump 14, and also, the oxygen partial pressure of this purifiedgas can be checked, enabling the gas having the oxygen partial pressurecontrolled to the target value to be stably supplied to the tank.Further, the oxygen sensors 15A and 15B are disposed upstream anddownstream of the oxygen pump 14, and hence it becomes easier toregulate the gas to be purified by the oxygen pump 14, with the resultthat a gas having the oxygen partial pressure controlled more accuratelycan be purified.

Next, FIG. 8 illustrates another embodiment, and, in this case, aplurality of (in the example of FIG. 8, two) gas purification sections21A and 21B are provided. Each of the gas purification sections 21A and21B has the same configuration as that of the gas purification section21 illustrated in FIG. 1, and hence a description thereof is omitted. Inthis unit as well, a circulation circuit 53 including the tank (buffertank) 20, the gas purification sections 21A and 21B, and the like isformed, and the purified gas stored in the tank 20 is supplied to thesample preparation chamber.

The circulation circuit 53 includes a purification circuit section 54including the gas purification sections 21A and 21B, a first connectingpipe 55 connecting the downstream side of the purification circuitsection 54 and the tank 20, and a second connecting pipe 56 connectingthe upstream side of the purification circuit section 54 and the tank20.

The purification circuit section 54 includes a pair of the gaspurification sections 21A and 21B disposed in parallel with each other,junction pipes 57 and 58 that connect the downstream sides of the gaspurification sections 21A and 21B, and branch pipes 59 and 60 thatconnect the upstream sides of the gas purification sections 21A and 21B.Switching valves 61, 62, 63, and 64 are interposed in the junction pipes57 and 58 and the branch pipes 59 and 60, respectively.

In the first connecting pipe 55, a flow rate regulating valve 65, a pump(for example, diaphragm pump) 66, and a switching valve 75 areinterposed. In the second connecting pipe 56, switching valves 67 and 68are interposed. A gas inflow pipe 69 in which a switching valve 74 isinterposed is connected to a junction portion of the branch pipes 59 and60, and the second connecting pipe 56 is connected to the gas inflowpipe 69 on the downstream side of the switching valve 74.

A gas outflow pipe 70 is connected to the second connecting pipe 56. Inthe gas outflow pipe 70, a switching valve 71, an REG 72, and an MFC 73are interposed. It should be noted that the gas outflow pipe 70 isconnected to the second connecting pipe 56 on the upstream side of theswitching valve 67.

Next, a description is made of an operation of the unit illustrated inFIG. 8. First, the source gas is stored in the tank 20. Specifically,the switching valves 61, 62, 63, and 64 of the purification circuitsection 54 are set to the open state, and the switching valves 67 and 68of the second connecting pipe 56 are set to the closed state. Further,the switching valve 71 of the gas outflow pipe 70 is set to the closedstate.

With this, the source gas that has entered the gas inflow pipe 69 flowsthrough the purification circuit section 54 and the first connectingpipe 55 to the tank 20, and the tank 20 is filled with the source gas.After that, the switching valve 74 of the gas inflow pipe 69 is set tothe closed state, and the switching valves 67 and 68 of the secondconnecting pipe 56 are set to the open state. With this, the gascirculates along the circulation circuit 53 including the tank 20, thesecond connecting pipe 56, the purification circuit section 54, and thefirst connecting pipe 55. This circulation enables the purificationcircuit section 54 to purify the gas having the oxygen partial pressurecontrolled within a range of from 0.2 to 10⁻³⁰ atm, and the gas filledin the tank 20 is purified.

In this manner, once the gas of the tank 20 is purified, this purifiedgas of the tank 20 can be supplied to the sample preparation chamber.Specifically, the switching valve 75 of the first connecting pipe 55 isset to the closed state, and the switching valves 67 and 68 of thesecond connecting pipe 56 are set to the closed state. Further, theswitching valve 71 of the gas outflow pipe 70 is set to the open state.Accordingly, the purified gas of the tank 20 flows out to the gasoutflow pipe 70, and the purified gas can be supplied to the samplepreparation chamber via the REG 72 and the MFC 73.

Incidentally, because the purification circuit section 54 is providedwith the pair of the gas purification sections 21A and 21B, the gas mayonly be purified by any one of them. Specifically, in a case where thegas is purified by the first gas purification section 21A and the secondgas purification section 21B does not purify the gas, the switchingvalves 62 and 64 have only to be set to the closed state. Further,conversely, in a case where the gas is purified by the second gaspurification section 21B and the first gas purification section 21A doesnot purify the gas, the switching valves 61 and 63 have only to be setto the closed state.

In the unit illustrated in FIG. 8, by using the switching valves 61, 62,63, and 64, and the like, it is possible to form a third switching means76 that switches between the permission and the suspension of the supplyof the purified gas to the tank from each of the gas purificationsections. With the switching of this third switching means 76, it ispossible to cause the gas to circulate through any gas purificationsection among a plurality of the gas purification sections.

With the unit illustrated in FIG. 8, which is provided with theplurality of the gas purification sections 21, it is possible toincrease the gas purification capacity, enabling stable supply of thepurified gas to another unit. For this reason, it is also possible tosatisfactorily handle a unit that requires a large amount of thepurified gas, making applications for the gas supply free fromlimitation.

In addition, with the switching of the third switching means 76, thenumber of the gas purification sections through which the gas is to becaused to circulate can be changed, and hence the purification capacityfor the gas can be changed. Thus, it is possible to perform an efficientoperation by changing the purification capacity in accordance with theamount of gas use of another unit of a supply target.

Further, though illustration thereof is omitted, as another embodiment,a plurality of the tanks 20 and a plurality of the gas purificationsections 21 may be provided. In this manner, by providing the pluralityof the tanks 20 and the plurality of the gas purification sections 21,it is possible to attain the functional effect of the unit illustratedin FIG. 1 and the functional effect of the unit illustrated in FIG. 8,and therefore it becomes possible to perform a more accurate operationin accordance with the amount of gas use of another unit of the supplytarget. This enables a high-efficiency operation, and the another unitis stably supplied with the purified gas, resulting in creation of highquality samples and the like.

Hereinabove, the embodiments of the present invention have beendescribed, but the present invention is not limited to theabove-mentioned embodiments, and a variety of modifications can be made.For example, in the oxygen partial pressure control unit illustrated inFIG. 1 and other figures, the number of tanks may be one or three ormore. In the case where three or more tanks are provided, the purifiedgas can be supplied to the sample preparation chamber or the like at thesame time from two or more tanks, or the purified gas can be stored intwo or more tanks. An operation can be selected from a variety ofoptions in accordance with the amount of gas use or the like. Further,in the oxygen partial pressure control unit illustrated in FIG. 8, threeor more gas purification sections may be provided.

Incidentally, in the above-mentioned embodiments, the oxygen sensors 15Aand 15B are disposed upstream and downstream of the oxygen pump 14, butthe upstream oxygen sensor 15A may be omitted. Specifically, the oxygenpartial pressure of the gas purified by the oxygen pump 14 only needs tobe checked and controlled to a desired value. Accordingly, thedownstream oxygen sensor 15B alone can sufficiently control the partialpressure to a desired value.

Further, in a case where there is no need to consider the generation ofimpurities in the sample preparation chamber or in a case wheregenerated impurities can be removed, the used purified gas dischargedfrom the sample preparation chamber may be returned to the gaspurification section 21 and recycled. If new supply gas is to be usedfor the whole of the inert gas to be supplied to the sample preparationchamber, in addition to the increased load on the oxygen pump 14 and theincreased size and cost for the installation, the installation spacebecomes larger and the cost for controlling the oxygen partial pressureto a predetermined value becomes higher as well.

However, the used purified gas discharged from the sample preparationchamber is obviously higher in oxygen partial pressure compared to thepurified gas that has been subjected to the oxygen partial pressurecontrol in the oxygen pump 14 and is supplied to the sample preparationchamber, but much lower in oxygen partial pressure compared to a newsupply gas that is supplied from a valve for inflow 2. Accordingly, if areturn pipe or the like is provided and the used purified gas dischargedfrom the sample preparation chamber is returned to the gas purificationsection 21 and recycled, compared to the case where only a new sourcegas is supplied, it is possible to not only reduce the amount of use ofthe supply gas but also reduce the load on the oxygen pump 14 andrealize downsizing and low pricing. Further, it is also possible toreduce the installation space and the cost for controlling the oxygenpartial pressure to the predetermined value.

INDUSTRIAL APPLICABILITY

The purified gas having the controlled oxygen partial pressure can besupplied to a die bonder, a solder proportioning ejection unit, or thelike. The die bonder is a unit that bonds a die (silicon substrate chipon which electronic circuits are manufactured) to a lead frame, a basematerial, or the like by using solder, gold plating, or resin as abonding material. Further, the solder proportioning ejection unit is adispenser that ejects a liquid material (solder) used forbonding/connecting, for example, electrical parts, electronic parts,precision parts, and the like.

1. An oxygen partial pressure control unit, comprising: a gaspurification section for purifying a gas having an oxygen partialpressure controlled within a range of from 0.2 to 10⁻³⁰ atm; and a tankfor storing the purified gas produced by the gas purification section,the oxygen partial pressure control unit supplying the purified gasstored within the tank to another unit, wherein the oxygen partialpressure control unit further comprises a circulation circuit comprisingthe tank and the gas purification section, and a source gas supplied tothe oxygen partial pressure control unit is caused to circulate alongthe circulation circuit, and the purified gas produced by the gaspurification section is stored in the tank.
 2. An oxygen partialpressure control unit according to claim 1, wherein: the circulationcircuit comprises: a plurality of the tanks; a first switching means forswitching between permission and suspension of supply of the purifiedgas produced by the gas purification section to each of the plurality ofthe tanks; and a second switching means for switching between permissionand suspension of supply of the purified gas of the each of theplurality of the tanks to the another unit; and the circulation circuitis configured to: switch the second switching means to permit the supplyof the purified gas from at least one of the plurality of the tanks tothe another unit; and switch the first switching means to permit thesupply of the purified gas to the tank that has finished the supply ofthe purified gas to the another unit, with the supply of the purifiedgas from the at least one of the plurality of the tanks permitted.
 3. Anoxygen partial pressure control unit according to claim 1, wherein: thecirculation circuit comprises: a plurality of the gas purificationsections; and a third switching means for switching between permissionand suspension of supply of the purified gas from each of the pluralityof the gas purification sections to the tank; and the circulationcircuit switches the third switching means to permit the gas tocirculate through a desired gas purification section among the pluralityof the gas purification sections.
 4. An oxygen partial pressure controlunit according to claim 1, wherein: the circulation circuit comprises: aplurality of the tanks; a plurality of the gas purification sections; afirst switching means for switching between permission and suspension ofsupply of the purified gas produced by the gas purification sections toeach of the plurality of the tanks; a second switching means forswitching between permission and suspension of supply of the purifiedgas of the each of the plurality of the tanks to the another unit; and athird switching means for switching between permission and suspension ofsupply of the purified gas from each of the plurality of the gaspurification sections to the plurality of the tanks; and the circulationcircuit is configured to: switch the second switching means to permitthe supply of the purified gas from at least one of the plurality of thetanks to the another unit; switch the first switching means to permitthe supply of the purified gas to the tank that has finished the supplyof the purified gas to the another unit, with the supply of the purifiedgas from the at least one of the plurality of the tanks permitted; andswitch the third switching means to permit the gas to circulate througha desired gas purification section among the plurality of the gaspurification sections.
 5. An oxygen partial pressure control unitaccording to claim 1, wherein the gas purification section comprises: anelectrochemical oxygen pump capable of controlling the gas to a targetoxygen partial pressure; and an oxygen sensor for monitoring the oxygenpartial pressure of the gas.
 6. An oxygen partial pressure control unitaccording to claim 5, wherein the oxygen sensor is a plurality of oxygensensors, at least one of the oxygen sensors being disposed upstream ofthe electrochemical oxygen pump and at least one other of the oxygensensors being disposed downstream of the electrochemical oxygen pump. 7.An oxygen partial pressure control unit according to claim 2, whereinthe gas purification section comprises: an electrochemical oxygen pumpcapable of controlling the gas to a target oxygen partial pressure; andan oxygen sensor for monitoring the oxygen partial pressure of the gas.8. An oxygen partial pressure control unit according to claim 3, whereineach of the gas purification sections comprises: an electrochemicaloxygen pump capable of controlling the gas to a target oxygen partialpressure; and an oxygen sensor for monitoring the oxygen partialpressure of the gas.
 9. An oxygen partial pressure control unitaccording to claim 4, wherein each of the gas purification sectionscomprises: an electrochemical oxygen pump capable of controlling the gasto a target oxygen partial pressure; and an oxygen sensor for monitoringthe oxygen partial pressure of the gas.
 10. An oxygen partial pressurecontrol unit according to claim 7, wherein the oxygen sensor is aplurality of oxygen sensors, at least one of the oxygen sensors beingdisposed upstream of the electrochemical oxygen pump and at least oneother of the oxygen sensors being disposed downstream of theelectrochemical oxygen pump.
 11. An oxygen partial pressure control unitaccording to claim 8, wherein, for each of the gas purificationsections, the oxygen sensor is a plurality of oxygen sensors, at leastone of the oxygen sensors being disposed upstream of the electrochemicaloxygen pump and at least one other of the oxygen sensors being disposeddownstream of the electrochemical oxygen pump.
 12. An oxygen partialpressure control unit according to claim 9, wherein, for each of the gaspurification sections, the oxygen sensor is a plurality of oxygensensors, at least one of the oxygen sensors being disposed upstream ofthe electrochemical oxygen pump and at least one other of the oxygensensors being disposed downstream of the electrochemical oxygen pump.13. A supply method of supplying, to another unit, a purified gas havingan oxygen partial pressure controlled within a range of from 0.2 to10⁻³⁰ atm, the supply method comprising: supplying, after storing thepurified gas in a plurality of tanks, the purified gas from at least oneof the plurality of tanks to the another unit; supplying, afterfinishing the supplying the gas from the at least one of the pluralityof tanks, the purified gas from another one of the plurality of tanks tothe another unit; and storing the purified gas in a tank that hasfinished supplying the purified gas during at least one of the supplyingof the purified gas.